Analysis of isolated sea urchin nuclei incubated in egg cytosol

Abstract

AbstractDuring fertilization the condensed sperm chromatin rapidly disperses and forms the male pronucleus. The possibility exists that substances which are concerned with chromatin dispersion may be present in the egg prior to insemination. To test for the presence of factors that may induce chromatin decondensation within the egg cytoplasm, a cell‐free system was devised in which isolated sperm nuclei were incubated in egg cytosol. Isolated sperm nuclei incubated in egg cytosol underwent nuclear enlargement and spherulation, i.e., increased at least three times that of the original volume of the sperm nucleus. This effect was potentiated, i.e., relatively more protein became associated with sperm nuclei, when sperm nuclei were treated with 0.25 N HCl to extract basic proteins prior to incubation in egg cytosol. Incubation in cytosol from Physarum, transformed NRK cells or Novikoff cells had no effect on the morphology of isolated sperm nuclei. Analysis of the proteins which became associated with acid‐extracted sperm nuclei showed that many had the same apparent molecular weight as those associated with male and female pronuclei. Analysis of egg cytosol proteins also indicated that many polypeptides had an affinity for DNA and the same apparent molecular weight as those associated with male and female pronuclei and zygote nuclei.